CRUD Operations with the ORM

CRUD stands for Create, Read, Update, Delete—the four basic database operations. Django's ORM makes these operations feel natural and Pythonic.

Using the Django Shell

The Django shell loads your project settings:

bash
python manage.py shell

python
>>> from polls.models import Question, Choice
>>> from django.utils import timezone

Create

There are several ways to create records:

Using save()

The most explicit way to create a record is to instantiate the model and then call save() to write it to the database.

python
# Create an instance
q = Question(question_text="What's new?", pub_date=timezone.now())

# Save to database
q.save()

# Now it has an ID
print(q.id)  # 1

Using create()

A more concise alternative is objects.create(), which instantiates and saves the object in a single step.

python
# Create and save in one step
q = Question.objects.create(
    question_text="What's your favorite color?",
    pub_date=timezone.now()
)

Creating Related Objects

When creating objects that reference another model via a ForeignKey, you can use the related manager or set the foreign key directly.

python
# Create choices for a question
q = Question.objects.get(pk=1)

# Method 1: Using create on the related manager
q.choice_set.create(choice_text='Red', votes=0)
q.choice_set.create(choice_text='Blue', votes=0)

# Method 2: Setting the foreign key directly
c = Choice(question=q, choice_text='Green', votes=0)
c.save()

Read

Django provides powerful query methods:

Retrieving All Objects

The all() method returns a QuerySet containing every record in the table.

python
# Get all questions
questions = Question.objects.all()
# <QuerySet [<Question: What's new?>, <Question: What's your favorite color?>]>

Retrieving Specific Objects

Use get() when you need exactly one object. It raises an exception if zero or multiple records match.

python
# Get by primary key
q = Question.objects.get(pk=1)

# Get by field value
q = Question.objects.get(question_text="What's new?")

# get() raises DoesNotExist if no match
# get() raises MultipleObjectsReturned if multiple matches

Filtering

The filter() method returns a QuerySet of objects matching the given conditions. You can chain multiple conditions for AND logic.

python
# Filter returns a QuerySet
Question.objects.filter(pub_date__year=2024)

# Multiple conditions (AND)
Question.objects.filter(
    pub_date__year=2024,
    question_text__startswith='What'
)

# Exclude
Question.objects.exclude(pub_date__year=2023)

Field Lookups

Use double underscores for lookups:

python
# Exact match (default)
Question.objects.filter(id=1)
Question.objects.filter(id__exact=1)  # Same as above

# Case-insensitive exact
Question.objects.filter(question_text__iexact="what's new?")

# Contains
Question.objects.filter(question_text__contains='favorite')
Question.objects.filter(question_text__icontains='FAVORITE')  # Case-insensitive

# Starts/ends with
Question.objects.filter(question_text__startswith='What')
Question.objects.filter(question_text__endswith='?')

# Date lookups
Question.objects.filter(pub_date__year=2024)
Question.objects.filter(pub_date__month=6)
Question.objects.filter(pub_date__gte=timezone.now())  # Greater than or equal

# In a list
Question.objects.filter(id__in=[1, 3, 5])

Ordering

Use order_by() to sort QuerySet results. Prefix a field name with - for descending order.

python
# Ascending
Question.objects.order_by('pub_date')

# Descending
Question.objects.order_by('-pub_date')

# Multiple fields
Question.objects.order_by('pub_date', 'question_text')

Update

Updating a Single Object

To update a single object, modify its attributes and call save() to persist the changes.

python
q = Question.objects.get(pk=1)
q.question_text = "What's up?"
q.save()

Updating Multiple Objects

For bulk updates, use QuerySet.update() which runs a single SQL query instead of saving each object individually.

python
# Update all choices to 0 votes
Choice.objects.filter(question__pk=1).update(votes=0)

Delete

Deleting a Single Object

Call delete() on a model instance to remove it from the database. Django returns a tuple showing what was deleted, including any cascaded deletions.

python
q = Question.objects.get(pk=1)
q.delete()
# (3, {'polls.Choice': 2, 'polls.Question': 1})
# Returns count and objects deleted (including cascaded)

Deleting Multiple Objects

You can also call delete() on a QuerySet to remove multiple objects at once.

python
# Delete all choices with 0 votes
Choice.objects.filter(votes=0).delete()

QuerySets are Lazy

QuerySets don't hit the database until evaluated:

python
# No database query yet
qs = Question.objects.filter(pub_date__year=2024)

# Database is queried when:
list(qs)           # Converting to list
for q in qs:       # Iterating
    print(q)
qs[0]              # Indexing
print(qs)          # Printing

Common Pitfalls

• Using get() when multiple objects might match: get() raises MultipleObjectsReturned if more than one object matches. Use filter() when you expect multiple results.
• Forgetting that QuerySets are lazy: No database query runs until the QuerySet is evaluated (iterated, sliced, or converted to a list).
• Not handling DoesNotExist: Always wrap get() calls in try/except or use get_object_or_404() in views.

Best Practices

• Use create() for single-step creation instead of instantiating and calling save() separately.
• Use update() for bulk updates instead of looping through objects and calling save() on each one.
• Chain QuerySet methods for readable queries: Question.objects.filter(...).exclude(...).order_by(...).

Summary

• Create objects with Model.objects.create() or instantiate and call .save()
• Read objects with all(), get() (single), or filter() (multiple)
• Update by modifying attributes and calling .save(), or use QuerySet.update() for bulk updates
• Delete with .delete() on an instance or QuerySet
• QuerySets are lazy and support chaining, field lookups (double underscores), and ordering

from polls.models import Question
from django.utils import timezone

# Create
q = Question.objects.create(
    question_text="What's your favorite color?",
    pub_date=timezone.now()
)

# Read
all_questions = Question.objects.all()
recent = Question.objects.filter(pub_date__year=2024)

# Update
q.question_text = "What's your favorite language?"
q.save()

# Delete
q.delete()